There are a variety of known ring mechanisms. Whilst a large number of different designs have been proposed, current ring mechanisms share a number of basic features or elements. Thus, the main body or base of the ring mechanism is provided by a cover rail, which is pressed from sheet steel. The cover rail has turned in side edges, and includes apertures adjacent the side edges for the ring elements. Additionally, the cover rail is provided with some means for mounting it, usually by rivets, to a ring binder or the like. Within the cover rail, there are a pair of carrier rails in nested side by side relationship. The width of the carrier rails is greater than the width between the sides of the cover rail, in an unstressed condition. Consequently, the carrier rails can be moved between open and closed over centre positions, the resiliency of the cover rail maintaining the carrier rails in these two positions. The ring elements are secured to the carrier rails and extend upwardly through the apertures of the cover rail. The ring elements are arranged in pairs, and each pair has a pair of complementary mesh ends that, in the closed over centre position mesh with one another.
In the development of ring mechanisms, numerous variance and alterations have been suggested. Thus, there have been proposals for a wide variety of different ring profiles. These include circular rings, rectangular rings, ring mechanisms having mixed profiles on either side for the ring elements, and a so-called "slant D" mechanism in which one ring element has a straight, sloping side. Additionally, proposals have been made for various modifications and configurations for the other elements.
At the present time, ring mechanisms are used for a wide variety of different purposes. Thus they can be used by students for storing notes, which can be readily inserted as the notes accumulate. Binder with ring mechanisms can also be used to store a variety of printed material. They are particularly convenient for storing reference material, which is frequently and regularly updated. Thus, there are organizations which need to maintain copies of official government regulations or publications, which are regularly updated. This is simply and easily accomplished, by using the loose leaf format in a ring binder. Then, when any one page is changed, only that page has to be replaced.
At the present time, ring binders (i.e. binders including ring mechanisms mounted within them for holding the sheets) are often used for holding relatively large and voluminous reference works. An example in the patent field is the use of such ring binders for holding patent examining manuals. In many cases, such reference works can contain many hundreds of pages, and consequently the mass or weight of paper is considerable. Equally, in the case of student notes and the like, it happens that a large mass of notes are accumulated and held witin one binder.
For large documents, particularly those with large sheets which are frequently used, sometimes ring mechanisms having more than the usual two or three pairs of ring elements are provided; for example, ring mechanisms sometimes have seven pairs of ring elements. This can increase the durability of the document. Damage to the individual sheets should be reduced, and in any event if only a few holes in any one sheet are damaged, the remaining holes will secure it in place. However, this sort of feature does not address the problem of securely retaining all of the sheets in position.
The ring elements are held in the closed position solely by the resiliency of the cover rail. The edges of the cover rail are held apart by the carrier rails, so that the cover rail in turn presses inwards to maintain the carrier rails in the closed over centre position. However, in the closed position, the inner edges of the carrier rails are only slightly lower than the outer edges thereof. As a consequence, there is a considerable mechanical advantage between the mesh ends of the ring elements and the carrier rails; i.e. a relatively large movement between the mesh ends produces a relatively small movement of the carrier rails.
Whilst in theory, the force needed to displace and open the mesh ends of the ring elements could be made as large as desired by suitable dimensioning of the components, as a practical matter it must be sufficiently low that the ring mechanism can be comfortably operated by the user. The mechanism is opened either by grasping the ring elements and pulling them apart, or by operating a pair of trigger or booster levers at either end that act on the carrier rails. Consequently, one cannot simply provide a heavier gauge cover rail, to ensure that the ring elements are securely held in the closed configuration, as the device may then not be usable.
Where the ring mechanism is dimensioned so that the forces required to open it are comfortable to the user, then it may not provide the required degree of security. Particularly where large and bulky documents or collections of papers are held, the ring mechanism can accidently burst open. This can happen where a binder is dropped or handled roughly, the inertial effect of the document can be sufficient to force the ring elements open. This releases the document, causing paper to be scattered. This can be a particular problem with large binders holding reference material in public locations, eg. libraries etc., where they may be subjected to abuse and not be handled carefully.
Accordingly, it is desirable that a ring mechanism should securely retain all papers at all times. This should be the case even for large and heavy volumes of paper. Simultaneously, the ring mechanism should still be capable of easy operation, permitting ready removal and insertion of pages.